Mask level reduction for MOSFET

Abstract

A method of fabricating a thin film transistor for an active matrix display using reduced masking operations includes patterning a gate on a substrate. A gate dielectric is formed over the gate and a semiconducting metal oxide is deposited on the gate dielectric. A channel protection layer is patterned on the semiconducting metal oxide overlying the gate to define a channel area and to expose the remaining semiconducting metal oxide. A source/drain metal layer is deposited on the structure and etched through to the channel protection layer above the gate to separate the source/drain metal layer into source and drain terminals and the source/drain metal layer and the semiconducting metal oxide are etched through at the periphery to isolate the transistor. A nonconductive spacer is patterned on the transistor and portions of the surrounding source/drain metal layer.

1. A method of fabricating a thin film transistor and transparent light transmission area for an active matrix display with reduced masking operations, the method comprising the steps of:
 providing a transparent substrate with a surface; 
 patterning gate metal on the surface of the substrate to define a thin film transistor gate; 
 forming a layer of transparent gate dielectric over the gate and surrounding substrate surface; 
 depositing a layer of transparent semiconducting metal oxide on the layer of gate dielectric; 
 patterning a channel protection layer on the semiconducting metal oxide overlying the gate, the channel protection layer being patterned to define a channel area in the semiconducting metal oxide above the gate and to expose the remaining semiconducting metal oxide; 
 depositing at least a source/drain metal layer on the channel protection layer and the exposed semiconducting metal oxide; 
 in a single etching step, etching through the source/drain metal layer to the channel protection layer above the gate to separate the source/drain metal layer into thin film transistor source and drain terminals and etching through the source/drain metal layer and the semiconducting metal oxide at the periphery to isolate the thin film transistor; 
 patterning a nonconductive spacer layer on the isolated thin film transistor and portions of the surrounding source/drain metal layer, the spacer layer defining a light transmission area adjacent the channel area designed to receive a light transmitting device in overlying relationship; and 
 using the patterned nonconductive layer as a mask etching through the source/drain metal layer in the light transmission area to expose the semiconducting metal oxide as a transparent pixel terminal contacting or forming one terminal of the overlying light transmitting device. 
 
     
     
       2. A method as claimed in  claim 1  wherein the fabrication of the thin film transistor includes fabricating a plurality of thin film transistors in an active matrix display, the active matrix display including a matrix of data lines and scan lines with the gate metal being connected to one of the scan lines and the source/drain metal being connected to one of the data lines. 
     
     
       3. A method as claimed in  claim 1  wherein the light transmitting device includes one of a liquid crystal device (LCD) and an organic light emission device (OLED). 
     
     
       4. A method as claimed in  claim 1  wherein the spacer layer is positioned to separate the substrate and associated components formed thereon from adjacent substrate formations in the active matrix display. 
     
     
       5. A method as claimed in  claim 1  wherein the step of depositing at least a source/drain metal layer includes depositing a layer of transparent oxide on the channel protection layer and the exposed semiconducting metal oxide prior to depositing the source/drain metal layer. 
     
     
       6. A method as claimed in  claim 5  wherein the step of depositing at least a source/drain metal layer includes depositing a barrier metal layer on the layer of transparent oxide. 
     
     
       7. A method as claimed in  claim 6  wherein the step of depositing the barrier metal layer includes depositing one of Mo, W, Cr, and Ni. 
     
     
       8. A method of fabricating a matrix of thin film transistors in an active matrix display, the active matrix display including a matrix of data lines and scan lines, the method comprising the steps of:
 providing a transparent substrate with a surface; 
 patterning gate metal on the surface of the substrate to define a gate for each thin film transistor of the matrix, and connecting the gate of each thin film transistor of the matrix to a selected scan line; 
 forming a layer of transparent gate dielectric over each of the gates and surrounding substrate surface; 
 depositing a layer of transparent semiconducting metal oxide on the layer of gate dielectric; 
 patterning a channel protection layer on the semiconducting metal oxide overlying each gate, the channel protection layer being patterned to define a channel area in the semiconducting metal oxide above each gate and to expose the remaining semiconducting metal oxide; 
 depositing at least a source/drain metal layer on the channel protection layer and the exposed semiconducting metal oxide; 
 in a single etching step, etching through the source/drain metal layer to the channel protection layer above each gate to separate the source/drain metal layer into thin film transistor source and drain terminals and etching through the source/drain metal layer and the semiconducting metal oxide at the periphery to isolate each thin film transistor of the matrix, and connecting each of the source/drain terminals to one of the data lines; 
 patterning a nonconductive spacer layer on the isolated thin film transistor and portions of the surrounding source/drain metal layer, the spacer layer defining a light transmission area adjacent the channel area designed to receive a light transmitting device in overlying relationship; and 
 using the patterned nonconductive layer as a mask etching through the source/drain metal layer in the light transmission area to expose the semiconducting metal oxide as a transparent pixel terminal. 
 
     
     
       9. A method as claimed in  claim 8  wherein the transparent pixel terminal in the light transmission area is an electrode of a light emission device in the active matrix display. 
     
     
       10. A method as claimed in  claim 9  wherein the light emission device includes one of a liquid crystal emission device (LCD) and an organic light emission device (OLED). 
     
     
       11. A method as claimed in  claim 9  wherein the spacer layer is positioned to separate the substrate and associated components formed thereon from adjacent substrate formations in the active matrix display. 
     
     
       12. A method as claimed in  claim 8  wherein the step of depositing at least a source/drain metal layer includes depositing a layer of transparent oxide on the channel protection layer and the exposed semiconducting metal oxide prior to depositing the source/drain metal layer. 
     
     
       13. A method as claimed in  claim 12  wherein the step of depositing at least a source/drain metal layer includes depositing a barrier metal layer on the layer of transparent oxide. 
     
     
       14. A method as claimed in  claim 13  wherein the step of depositing the barrier metal layer includes depositing one of Mo, W, Cr, and Ni.